Filter-tipped smoking articles, particularly cigarettes, generally comprise a tobacco rod, a filter and a band of tipping paper attaching the filter to tobacco rod. The tobacco rod generally comprises a column of shredded tobacco (e.g., in form of cut filler) that is wrapped within a cigarette paper or wrapper. Typically, the filter includes a plug of fibrous material (a “filter plug”), preferably made of a cellulose acetate tow. Ventilation of mainstream smoke is achieved by provision of a row or rows of perforations through the tipping paper at a location along the filter plug. Ventilation provides dilution of drawn mainstream smoke with ambient air to reduce the delivery level of tar per puff.
During smoking, a smoker draws mainstream smoke from the coal at the lit end of the cigarette. The drawn cigarette smoke first enters the upstream filter portion of the filter and then passes through the downstream portion adjacent to the buccal end of the cigarette filter.
Certain cigarettes have filter segments which incorporate materials such as granules of carbon, silica gel, zeolite and the like. Exemplary cigarettes and filters are described in U.S. Pat. Nos. 2,881,770 to Tovey; 3,353,543 to Sproull et al.; 3,101,723 to Seligman et al.; and 4,481,958 to Ranier et al. and European Patent Application Nos. 532,329 and 608,047. Certain commercially available filters have particles or granules of carbon (e.g., an activated carbon material) alone or dispersed within a cellulose acetate tow; other commercially available filters have carbon threads dispersed therein; while still other commercially available filters have so-called “cavity filter” or “triple filter” designs. Exemplary, commercially available filters include SCS IV Dual Solid Charcoal Filter and Triple Solid Charcoal Filter from Filtrona International, Ltd.; Triple Cavity Filter from Baumgartner; and ACT from Filtrona International, Ltd. See also, Clarke et al., World Tobacco, p. 55 (November 1992). Detailed discussion of the properties and composition of cigarettes and filters is found in U.S. Pat. Nos. 5,404,890 to Gentry et al. and 5,568,819 to Gentry et al., the disclosures of which are hereby incorporated by reference.
Examples of concentric filter layouts that include granular carbon are disclosed in European Patent Application No. 579,410 and U.S. Pat. No. 3,894,545 to Crellin et al.
The plug-space-plug design typically comprises a pair of spaced-apart filter plugs and a bed of granulated, activated carbon in the cavity or space therebetween. In their manufacture, a procession of spaced-apart filter plugs is established along a continuous ribbon of plug wrap. The plug wrap is then partially folded about a portion of the plug precession and granulated carbon material is poured or otherwise introduced into the spaces defined between the partially enwrapped filter plugs. The plug wrap is then glued and closed, and the resultant continuous rod is then cut in well-defined locations according to a desired length, usually in the form of multiples of the filter element actually utilized on the filter-tipped cigarette itself.
Cavity filling apparatus known in the art may be utilized in the manufacture of filter components such as shown in FIGS. 1 and 2. U.S. Pat. Nos. 4,214,508, 5,221,247, 5,322,459, 5,542,901 and 5,875,824 illustrate and describe such cavity filling apparatus and these disclosures are incorporated herein by reference.
With machines and carbon materials of the prior art, process control usually suffered at high machine speeds from inconsistent metering, scattering and pulverization of the granular material. Consistency amongst filter rods would suffer, and some cavities would be less filled than others.
For example, certain prior “charcoal” metering devices contain a supply of granular carbon in a hopper and allowed the rim of a rotating metering wheel to rotate through the relatively stationary collection of granular carbon. Such an arrangement created a pulverizing action upon the granular carbon, which action generally increased with machine speed. Ricochet and escape of particulate matter during manufacturing operations with prior machines and materials often created unacceptable deficiencies in the final product (such as smears or incomplete fillings) and precipitate undesirable machine “down-times” to effect clean-up of the machine and the surrounding work environment.
Granulated carbon, being a collection of irregularly shaped and variously sized particles, tends to pack into a given volume of space inconsistently from one filling operation to the next. Accordingly, heretofore incomplete and inconsistent filling of cavities would plague automated filter rod making. The irregular packing would also create undesirable channels through the bed that would allow passage of substantial portions of mainstream smoke through or around the bed such that interaction between the mainstream smoke and the granular carbon would be lessened.
It has been known to include granulated, activated carbon materials in cigarette filters to promote removal of constituents from mainstream smoke. As used heretofore in cigarette filters, these granular forms of carbon have been constructed by carbonizing an organic material such as nut shells or a wood material, and “activating” the carbonized material by subjecting it to a heat treatment at approximately 800 to 1000 degrees Celsius with steam or carbon dioxide. The activation treatment of the material results in a porous (honeycomb-like) internal structure and a very large specific surface area, typically in the range of 300 to 2500 square meters per gram as measured by the Brunauer, Emmett & Teller (“BET”) method for activated carbon.
However, such granulated, activated carbon materials have surface roughness and shapes which are irregular and inconsistent from granule to granule. These irregularities and inconsistencies of granulated carbon materials create problems in the commercial production of carbon-bearing cigarette filter rods and cigarettes. For example, the irregular shapes exacerbate ricochet of the particles as they are fed through filter rod making machines, which event dirties the product with errant carbon particles, puts dust into the work environment and creates a need for a shut-down to clean the rod making machine and leads to inconsistent and less complete filling of the cavities in the plug-space-plug filter rods.
Granulated, activated carbon materials also are known to have a significant impact on the taste of a cigarette, in that their randomly broad range of pore size distribution tends to capture not only gas phase components of a mainstream tobacco smoke, but also portions of the particulate phase, i.e., some or a great number of tar constituents that contribute taste and flavor to the cigarette smoke. Granular activated carbons that are constructed from nut shells or wood are also known to include impurities, which are believed to be another possible cause of off-tastes attributed to the use of granulated carbon in cigarettes.
It is also understood that the process of activating granular carbon tends to weaken the granule body, such that it is less robust and more prone to fracture, pulverization and dusting when fed through metering devices of filter rod making machines. It is also understood that the activation treatment adds cost to the manufacture of granulated material.